You will need the following for an outdoor painting session.
Organise your equipment well in advance in a large bag or backpack:
Canvas or canvas panels
Paints
Brushes
Palette (or a plate on which to mix paints)
Easel
Stool (unless you want to stand)
Containers for water for mixing and cleaning (acrylic)
Oil and turps for mixing and cleaning (oils)
Sketch pad and pencil
A camera
Rags or paper for cleaning
Bag for ALL rubbish
Outdoor clothes for cold or showery weather
Sun protection
If you are travelling to an isolated location consider bringing food and drinks